Affordable Infrastructure for Stream Playback in the Internet
Key: GJZ99-1
Author: Carsten Griwodz, Alex Jonas, Michael Zink
Date: December 1999
Kind: @techreport
Abstract: The increasing amount of audio-visual (AV) content that is offered by web sites leads to a network bandwidth and storage capacity problem. Caching is one of the techniques that can ease this problem. But even in a caching system the distribution of data (i.e. the AV content) should be bandwidth-efficient in order to preserve the advantages of caching. Furthermore the delivery to the end-user must regard the restrictions implied by real-time data. This paper describes LC-RTP, an efficient and simple reliable multicast protocol that complies with RTP. LC-RTP provides lossless transmission of AV content into cache servers and concurrently, real-time delivery to end-users using multicast. It achieves reliability by detecting loss of data and requesting retransmissions after the main session. Therefore the sender transmits the packets with some additional information and listens after the session for any loss requests of the receivers. The retransmission requests list contains ranges of byte counts which can be sent immediately after the main session regarding a sender-defined strategy. This ensures a minimal traffic increase because the transmission of the AV content and any caching will take place while the end-user is served, so dedicated transmissions to the cache are unnecessary. Support for multicast in the distribution system ensures that all cache servers of a multicast group can cache an AV content while transmitting it to a consumer. Whether a server caches a content or not depends on a caching strategy that is chosen independently. The paper presents a consistent protocol set by combining LC-RTP with the protocols RTSP and SDP that are used for stream control.
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